Authorities have arrested a Mexican army captain and a soldier as a video emerged showing a woman being tortured by troops and a federal police officer, officials said Thursday.

The attorney general's office has launched a torture investigation while military authorities have charged the captain and a female soldier with disobeying orders.

The jarring clip circulating online shows a female soldier placing the tip of her assault rifle on the woman's head as she sits barefoot on a dirt floor.

A federal police officer then tightly wraps a plastic bag around the woman's head while one of the officials asks her, "Are you going to talk?"

The woman, who is sobbing throughout the ordeal, answers: "Who's Maria? I don't know her."

It is the latest allegation of abuse committed by the authorities in Mexico.

The defense ministry said the incident took place in February 2015 in the town of Ajuchitlan del Progreso, in the southern state of Guerrero, but that it only learned about it in December.

The ministry said in a statement that the captain and the female soldier, who is part of the military police, were detained in January on charges of disobeying orders.

The attorney general's office issued a separate statement saying that its special torture investigations unit began its inquiry on January 7.

The unit is investigating the "probable responsibility of Mexican army members as well as a federal police officer who presumably participated" in the incident, the statement said.

The attorney general's office said that "in this, like in every case, it will act with all the rigor that the law permits to prevent impunity in any illegal conduct."

The federal police said its internal affairs department launched an investigation and it urged citizens to report any abuse by officers.

- History of abuses -

Amnesty International said the video shows that torture remains a technique for authorities to obtain coerced confessions.

"Ending the role of the armed forces in police work is urgent," said Perseo Quiroz Rendon, Amnesty's Mexico director, adding that troops lack the training to conduct investigations and interrogations.

Police and troops have faced a slew of accusations of torture and other abuses since soldiers were deployed in the streets of Mexico to combat drug trafficking in 2006.

A soldier has been detained in connection with the February disappearance and murder of a civilian in the eastern state of Veracruz.

In a separate case in the same region, eight state police officers were charged over the January disappearance of four young men and a 16-year-old girl.

And in another high-profile case, a military court in October acquitted seven soldiers who were detained following the killing of 22 alleged drug gang members in the central state of Mexico in June 2014.

Authorities had initially reported the deaths as resulting from a shootout, but allegations of extrajudicial killings emerged later.

Three of the soldiers still face murder charges in civilian court for the deaths of eight of the 22 suspects.